Calculate the percentage of water of crystallization in the sample of washing soda,${\mathrm{Na}}_2{\mathrm{CO}}_3.10 {\mathrm{H}}_2\mathrm{O}.$

An inorganic salt on analysis gave the following percentage composition: $\mathrm{Pb}=62.6$, $\mathrm{N}=8.4$, $\mathrm{O}=29$.

What is empirical formula of the compound? Also name the compound. (At. Mass: $\mathrm{Pb}=207, \mathrm{N}=14, \mathrm{O}=16$).

A sample of a salt has the percentage composition: $\mathrm{Fe}=36.76; \mathrm{S}=21.11; \mathrm{O}=42.14;$

Calculate the empirical formula of the compound. (At. Mass: $\mathrm{Fe}=56; \mathrm{S}=32; \mathrm{O}=16;$).